Drinking water scarcity in coastal areas – prediction and decision support tools

Robert Earon and Bo Olofsson, Royal Institute of Technology (KTH)

Aim of the project

The aim of this project is to improve understanding regarding groundwater in hard rock coastal regions. The study focuses on developing support tools for decision makers who are tasked with managing limited water supply resources in coastal regions and improving knowledge of the kinematic (effective) porosity values of hard rock. In hard rock terrains heterogeneity in the fracture network and geology limit the application of point-based hydrogeological tools. This study aims to develop methodologies which rely on continuous digital data (such as geological maps, topography, landuse) or simple field measurements of kinematic porosity which can complement existing data.

Status of the project

The project currently has three primary deliverables. The first is a study based on the development of a new methodology which uses geological indicators (such as distance to lineament, distance to water, soil type, bedrock type) in order to estimate the groundwater resource potential (GRP) of an area. This study uses analysis of variance (ANOVA) and principal component analysis (PCA) to generate regional GRP maps which correlate with specific capacity values estimated from the Geological Survey of Sweden’s well archive with more than 95% confidence. Parameters are classed according to a positive or negative influence on specific capacity estimates using ANOVA. PCA is then used to weight the different parameters by identifying the principal components which are most influenced by specific capacity and then weighting the other parameters based on their loadings on these components. Finally, classes and weights are combined to produce a statistical indicator of the GRP of a particular area.

Figure 1: An example of a groundwater resources potential (GRP) map from Vallentuna and Tyresö
Figure 1: An example of a groundwater resources potential (GRP) map from Vallentuna and Tyresö

The second scientific deliverable of this project is a study which uses superficial fracture measurements to estimate local kinematic porosity values. Estimates are based on a geometric model which incorporates hydraulic aperture, fracture spacing and orientation, as well as length of fracture and type. Results show that the estimates of porosity correlate with hydrogeogical indicators such as specific capacity. Finally, the last part of this project is a water balance methodology which is specifically customized for Swedish terrain. The method accounts for the limited storage values which are often found in Swedish coastal regions, and attempts to spatially account for well extraction in order to implement water balance calculations. Rather than making regional simplifications which often overlook pockets of soil which have porosity values orders of magnitude higher than crystalline bedrock, the method calculates storage, extraction and recharge locally in order to best account for the extreme heterogeneity typical to Swedish coastal regions.

Spin-off

Swedish coastal community planners as a rule have limited resources with which to manage their water reservoirs. The methods presented in this synopsis illustrate three new approaches to groundwater characterization which do not rely on large amounts of data or over simplifications which often hinder engineering solutions to such problems. Instead, the methods rely on easily collected data or existing digital datasets. The methods are executed in a GIS environment, and can directly contribute to aiding municipal planners in water resources management.